This invention relates to a fluid pumping system and, more particularly, to a fluid pumping system adapted for use with a natural gas dehydrating system of the type employed at a gas well head to remove water from a well stream composed of a mixture of gas, oil and water.
Examples of such gas dehydrating systems are disclosed in U.S. Pat. Nos. 3,094,574; 3,288,448; and 3,541,763; the disclosures of which are specifically incorporated herein by reference. In general, such systems comprise a separator means for receiving the gas-oil-water mixture from the well head and separating the oil and water liquids from "wet" (water vapor laden) gas; and a water absorber means, which employs a liquid dehydrating agent such as glycol, for removing the water vapor from the wet gas and producing "dry" gas suitable for commercial usage. The glycol is continuously supplied to the absorber means in a "dry" low water vapor pressure condition and is removed from the absorber means in a "wet" high water vapor pressure condition. The wet glycol is continuously removed from the absorber means and circulated through a reboiler means for removing the absorbed water from the glycol to provide a new supply of dry glycol. The glycol reboiler means usually comprises a still column associated with a gas burner for heating the wet glycol to produce hot dry glycol by removing the absorbed water by vaporization. The hot dry glycol passes through a heat exchanger, where the hot dry glycol is cooled and the incoming wet glycol is heated, to a dry glycol storage tank. A glycol passage means is provided to enable passage of wet glycol from the absorber means to the reboiler means and to pump dry glycol from the storage tank to the absorber means.
As described in our copending U.S. patent application, Ser. No. 36,839, filed May 7, 1979, the disclosure of which is hereby incorporated herein by reference, motors for glycol pumps of natural gas dehydrating systems have heretofore been designed to be operated by the energy of natural gas available at the well head due to the relatively high pressures and temperatures thereof. In addition, the energy of the wet glycol has been used to drive a single piston pump for the dry glycol as disclosed in U.S. Pat. No. 3,093,122 to Sachnik dated June 11, 1963. This pumping unit uses a fluid driven power piston, and a pilot valve driven by the same fluid controls the rate of operation of the master slide valve, which distributes fluid to the piston pump.
One of the problems with such prior pump designs is that the pressure of the gas stream from natural gas wells is highly available and gas operated pumps often require large amounts of energy. Furthermore, changes in gas pressures during day to day operation have often caused stalling of the pump and interruption of the entire dehydrating system. Since the dehydrating systems are continuously operated at the well site without continuous monitoring by operating personnel, reliable continuous operation of the pump is of critical importance.
Another important performance factor is that the pump be self-regulating to automatically adjust the pumping rate in accordance with available gas pressure and flow rates. In addition, it is highly desirable to use energy sources available at the well site for operation of the pump with maximum efficiency and minimum energy loss.
Thus, an object of the present invention is to provide a new improved glycol pumping system which is operated by an available energy source other than the saleable dry natural gas at the well head.
Another object is to provide a new and improved pump which may be operated at relatively low speeds and pressures without stalling.
Another object is to provide a pumping system which is automatically continuously operable under a wide range of operating conditions.
Another object of the invention is to provide a combined fluid operable motor and fluid pump of the piston type, having a gas operated controller for controlling the rate of reciprocating movement of the pump motor.
Still another object of the invention is to utilize minimum quantities of gas for the control of a fluid motor.
Yet another object of the invention is to provide a highly efficient motor-pump arrangement using high pressure wet glycol to pump dry glycol in various systems.
An additional object of the invention is to utilize the control gas discharged from the control gas motor controller in operation of the reboiler burner.
The foregoing objects have been achieved by utilizing the energy available in the wet glycol as the primary motivating force to drive a new and improved dry glycol pump apparatus including an automatic speed control means operably by a wide range of pressurized natural gas which can also provide a secondary motivating force for the pump apparatus. The pump apparatus comprises a pump means for pumping dry glycol from the dry glycol tank to the absorber; a primary motor means for operation by high energy wet glycol received from the absorber and exhausting low energy wet glycol to the reboiler means; and a combination secondary motor means and speed control means operable by dry natural gas and exhausted to the reboiler burner means.